1. Field of the Invention
This invention relates to a fuel-supply control system for a gas-turbine engine, wherein fuel-metering valves are driven by an electric pulse train so as to open periodically while the duty cycle of the pulse train is varied with a certain engine operating condition so that the amount of fuel supplied to the engine responds to the engine operating condition.
2. Description of the Prior Art
In a known fuel-supply control system for a gas-turbine engine, a fuel-metering valve controls the amount of fuel injected into the engine combustion chamber through a fuel injector. When the control valve opens, fuel flows therethrough to be injected through the injector. Since a pressure regulator controls the fuel pressure so as to keep the fuel flow rate constant when the control valve is open, the amount of fuel injected is proportional to the time during which the control valve is open (the time is hereinafter referred to as an open time of the valve). Generally, the control valve is of the electrically-driven type which opens when energized, and is driven by an electric pulse train so as to open periodically. Thus, the amount of fuel injected per a unit time, or the time-averaged fuel injection rate, depends on the duty cycle of the pulse train corresponding to the time rate of the control valve being open. Meanwhile the duty cycle of the pulse train is varied with a certain engine operating condition, such as a power required from the engine (hereinafter referred to as an engine required power) or an engine load so that the amount of fuel injected per a unit time responds to the engine operating condition.
When the engine is operated under constant conditions, such a fuel-supply control system may produce therein relatively large fuel pressure pulsations. Each opening of the control valve causes a fuel pressure pulsation, which travels back and forth within the system like a wave until being completely damped. In the above constant conditions, the control valve usually opens periodically at a constant frequency for a constant time, so that the fuel pressure pulsations may interfere with each other to form relatively large fuel pressure pulsations. The resultant large fuel pressure pulsations severely disturb the regulated pressure of the fuel injected, thereby lowering the stability of the accuracy of the control of the amount of fuel injected per a unit time.